Nearly a thousand drivers failed roadside drugs tests over the festive period, figures show.
A total of 1,888 motorists across the UK were stopped and screened for drug use during December, of which 931 tested positive.
"It's good to see the new drug-driving law is being enforced, but it is worrying that the December campaign caught so many motorists breaking the law with 50% of those tested proving to be over the limit," says RAC chief engineer David Bizley.
"Clearly, this kind of testing needs to be carried out constantly to help reduce the number of motorists who are prepared to drive having taken illegal or prescription drugs that impair safe conduct at the wheel."
Last spring, new regulations aimed at stopping people driving while under the influence of drugs came into force in England and Wales.
Police can now use "drugalyser" devices at the roadside to check for the presence of eight illegal drugs, including cannabis and cocaine, and eight prescription drugs.
"Regrettably, our research shows a sizeable minority of motorists (37%) do not believe the new law will reduce the number of drug-drivers on the roads. This is largely because drug-drivers are viewed as risk-takers and so more likely to ignore such a law and risk being caught," adds Mr Bizley.
"Findings from the RAC Report on Motoring also confirmed once again that drug-drivers are much more likely to be drink-drivers. Of the 6% who admit to driving under the influence of drugs, two-thirds (4%) also claim to have driven under the influence of alcohol.
"If a police officer suspects that a motorist is driving under the influence of both drink and drugs, they will normally test for alcohol only because this is far cheaper and simpler than testing for illegal drugs and the penalties are similar for both offences. The figures published by the police for positive drug tests are therefore likely to understate the number of motorists caught when driving under the influence of drugs."
Copyright Press Association 2016. Motoring News articles do not reflect the RAC's views unless clearly stated.